The present invention relates to an active matrix liquid crystal color display panel having a triangular arrangement of picture elements, and more particularly to a color liquid crystal display panel with redundancy of matrix elements.
Among various types of color display panels the active matrix color display panel in which thin film transistors are used as switching elements has the best image quality.
The active matrix comprises a plurality of picture elements arranged on a transparent insulating substrate in a matrix of lines and columns, each picture element comprising at least one display electrode and one switching transistor.
The matrix further comprises a plurality of address buses disposed between the lines of picture elements and a plurality of data buses disposed between the columns to cross orthogonally the address buses. The display electrodes are connected to the address lines and the data lines via a switching thin film transistor.
Address signals are applied to the thin film transistors (TFTs) whereas video signals are applied to the data buses to be applied to selected ones of the display electrodes via the TFTs turned on by the address signals.
In a color display one picture element comprises at least three picture elements for transmitting primary color components. Therefore, in comparison with a black-and-white display the number of required elements of the cells is three times as large.
The quality of color image depends, to a great extent, on the mutual arrangement of color picture elements.
FIG. 1 is a circuit diagram of a well-known active matrix color liquid crystal display panel. As shown in FIG. 1, the color liquid crystal display panel comprises a plurality of arrays 100 arranged in a matrix of rows and columns. The matrix comprises a plurality of data buses 1 and a plurality of address buses 2. Each picture element denoted by the reference numeral 31 has two display electrodes 3 and 4 disposed on both sides of the corresponding data bus 1 and two switching transistors 5 and 6 respectively connected to the display electrodes 3 and 4. The display electrodes 3 and 4 receive a video signal via the data bus 1 and the switching transistors, TFTs 5 and 6, respectively.
The sources of the switching transistors 5 and 6 are connected to the corresponding display electrodes 3 and 4, respectively. The drains of the switching transistors 5 and 6 are connected in common to the data bus 1 running between the display electrodes 3 and 4. The gates of the switching transistors 5 and 6 are connected in common to a corresponding one of the address buses 2. The display electrodes 3 and 4 are arranged on both sides of the address bus 2, respectively. Each pair of display electrodes 3 and 4 connected to an optional one of data buses 1 is disposed on one side of the corresponding address bus 2 forming lines of picture elements while each corresponding pair of the display electrodes connected to the neighboring data bus 1 is disposed on the other side of the address bus 2.
The display electrodes 3 and 4 labeled as R, G and B are covered with red, green and blue filters, respectively, to constitute color picture elements 31. In the lines 32 of picture elements 31 parallel to the address buses 2, the arrangement of the filters is repeated in the following order: red (R), blue (B) and green (G). The arrangement of the filters is shifted between two neighboring data lines 1 by a half pitch of the repetition cycle of the color filters to form triangular color picture elements which are constituted by two pairs of display electrodes in one line 32 and one pair of display electrodes in a neighboring line 32. Such an arrangement of color elements provides a high quality image.
However, this array design has an essential drawback that an open circuit in one of the data buses 1 or the address buses 2 results in a loss of operability of all picture elements coupled to the detective bus. In other words, the open circuit causes the appearance of line defects in the imaged picture.
There is also known an active matrix liquid crystal color display panel having a triangular arrangement of picture elements which is capable of avoiding a degradation of a high quality image under the influence of a small number of open circuits in the address buses.
Such a panel is illustrated in FIG. 2. Similar to the case of FIG. 1, the panel of FIG. 2 comprises a plurality of arrays 100 arranged in a matrix of rows and columns. Each array 100 comprises a plurality of address buses 1, a plurality of data buses 2 crossing orthogonally the address buses 1, and a plurality of picture elements 31 each constituted by two display electrodes 3 and 4. The display electrodes 3 and 4 of each picture element 31 are connected, via a first pair of switching transistors 5 and 7 and another pair of switching transistors 6 and 8, respectively, to a data bus 2 running between the display electrodes 3 and 4 of the picture element 31 and to two neighboring address buses 1.
The panel of FIG. 2 includes a plurality of red (R), green (G) and blue (B) filters each of which covers two display,electrodes and transmits a predetermined color component. The color filters in combination with the display electrodes are disposed to provide a triangular arrangement of picture elements as shown by the shaded regions in FIG. 2.
Thus, since the color liquid crystal panel has a triangular arrangement of picture elements of different colors, a high quality image can be obtained. Besides each picture element getting a video signal from one data bus via two switching transistors, it is connected to two different address lines by gates of the switching transistors. Therefore, if the address line has an open circuit, the video signal can be supplied to the picture electrode via the switching transistor connected to another address bus. So, the appearance of a small number of open circuits in the address buses does not cause line defects on the picture.
However, this design of color liquid crystal display panel has drawbacks that an open circuit in any of the data buses results in a loss of operability of all picture elements coupled to the defective part of the bus and that the open circuit causes the appearance of line defects on the imaged picture, thereby deteriorating the picture quality. A failure occurring in a considerable number of parts of picture element columns may cause the rejection of the whole panel resulting in a reduction in production yield.